We propose to investigate whether blood-retinal barrier changes occur at the retinal pigment epithelial cell layer in dystrophic and diabetic retinopathies. We will analyze intracellular transport of large molecular weight substances by dystrophic as compared to normal RPE cells. RPE explants at different postnatal ages will be exposed from the apical surface to horseradish peroxidase, native or cationized ferritin. Uptake and intracellular routes of the tracers will be analyzed with the electron microscope. We will study mechanisms of active intracellular transport in the dystrophic and normal rat RPE using electron microscope cytochemistry to localize Na+,K+, ATPase. We will investigate RPE cell junction permeability and intramembrane structure in diabetic and normal rats using lanthanum nitrate and freeze-fracture electron microscope techniques. We will characterize filtration barriers in the choroid-Bruch's membrane interface in normal and diabetic retinas using electron microscope tracer techniques (ruthenium red and native and cationized ferritin) which have been used to characterized filtration barriers in the renal glomerulus. The long-term objectives of our research are to determine the basic mechanisms of blood-retinal barrier changes and the relationship of such changes to retinopathy. It is anticipated that such data will contribute to the prevention of and/or treatment of blood-retinal barrier pathology.